.pos-center(@width){
  position: absolute;
  left: 50%;
  margin-left: -@width/2;
}
.pos-vertical(@height){
  position: absolute;
  top: 50%;
  margin-top: -@height/2;
}
.pos-c-v(@width,@height){
  position: absolute;
  left: 50%;
  top: 50%;
  margin-left: -@width/2;
  margin-top: -@height/2;
}